Technician Licensing Class

1
Technician Licensing Class
Lesson 4

• presented by the
• Midland Amateur Radio Club
• Midland, Texas

2
QuizSubelements T6 T7
3
Good Engineering PracticeSubelement T8
4
A Basic Station
Antenna
Feed Line
T-R Switch
Receiver
Transmitter
Power Supply
5
Simple CW Transmitter
Antenna

• Block 1 controls the frequency of the transmitter
• If Block 1 is a crystal it is referred to as a
  crystal controlled transmitter
• If Block 1 is a variable-frequency oscillator it
  is referred to as a VFO controlled transmitter
• CW is transmitted by on/off keying of the RF
  signal with the telegraph key.

6
Frequency Modulation (FM)
Unmodulated carrier, full power at all times
Waveform of modulating signal
Modulated carrier with frequency deviation and
constant amplitude
7
FM Transmitter
CLIPPER FILTER
AUDIO AMP
BLOCK 1
MULTIPLIER
MIC
OSCILLATOR
POWER AMP
MULTIPLIER
MULTIPLIER

• In an FM transmitter, Block 1 represents a
  Reactance Modulator.
• The Reactance Modulator changes the phase or
  frequency of the oscillator in response to the
  audio input.

8
FM Transmitter
CLIPPER FILTER
REACTANCE MODULATOR
AUDIO AMP
MULTIPLIER
MIC
OSCILLATOR
POWER AMP
MULTIPLIER
MULTIPLIER
If the Audio Amplifier in this FM transmitter
failed the output would be an unmodulated carrier.
9
Frequency Modulation

• FM transmitters operate at full power at all
  times, even with no audio input.
• When an FM transmitter over-modulates, the
  transmitted signal becomes so wide (bandwidth) it
  may cause out-of-channel emissions and interfere
  with adjacent channels. This is called
  over-deviation.
• If you are told you are over deviating you can
  talk farther away from the microphone.
• FM is effective for local VHF/UHF communications
  because the audio is less affected by static-type
  electrical noise.

10
Simple CW SSB Receiver
Product Detector

• The Mixer shifts the received signal frequency to
  an Intermediate Frequency (IF) for processing.
• The IF Amplifier adds gain and filtering.
• Many receivers have several IF filters of
  different bandwidths because some emission types
  need a wider bandwidth than others.
• The Product Detector mixes the IF with the Beat
  Frequency Oscillator (BFO) and restores the
  carrier and recovers the audio.

11
FM Receiver
Intermediate Frequency Amplifier
Radio Frequency Amplifier
Wide Filter
Mixer
Oscillator
Audio Amplifier
1
Limiter
Discriminator

• The IF Amplifier and Limiter remove unwanted
  amplitude variation.
• The Discriminator recovers the modulation signal
  from the Frequency Modulated IF signal.
• If a receiver has a DISCRIMINATOR it is an FM
  receiver.
• If the discriminator FAILS there is no audio
  output.

12
FM Receiver
This receiver could receive signals on 147.0 MHz
or 168.4 MHz. 157.7 MHz Oscillator minus 10.7
Mhz IF 147.0 Mhz or 157.7 MHz plus 10.7 MHz
168.4 MHz
13
FM Receiver

• This is a single-conversion superhetrodyne
  receiver because it has only one IF stage.
• This is an FM receiver because it has a
  DISCRIMINATOR.
• FM receivers have a SQUELCH which should be set
  at the point that it just silences background
  noise.

14
Receivers

• All receivers have a detector circuit function.
• In a CW/SSB receiver it is called a product
  detector
• In an FM receiver it is called a discriminator.
• One way to accurately check a receiver's tuning
  accuracy is to tune into one of the frequencies
  of station WWV or WWVH.
• Transmits the time and other information on
  exactly 2.5, 5, 10, 15, 20 MHz.

15
VHF / UHF Multimode Transceiver

• VHF / UHF transceivers are available which will
  operate on FM as well as AM, SSB, and CW.
• These transceivers are well suited for
  weak-signal communications work.

16
Data Communications - Packet

• Packet uses a terminal node controller (TNC) to
  interface a computer and transceiver.
• A TNC breaks the data to be transmitted into
  packets which includes error checking
  information.
• On VHF an FM transceiver may be used for packet.
• Since packet uses data carrier detect the
  receiver's squelch must be set to quiet the noise
  or the TNC may falsely detect a data carrier.

Packet
TNC
Transceiver
Computer
17
Data Communications - RTTY
RTTY

• A modem and teleprinter or computer are connected
  to a transceiver for RTTY operation.
• An FM transmitter could be used for RTTY on the
  VHF / UHF bands.
• RTTY transmits in a continuous stream and has no
  error checking.

Computer or Teleprinter
Modem
Transceiver
18
Station Accessories

• A power supply converts 120 v AC to 12 v DC and
  is necessary to run a mobile transceiver in the
  house.
• A 12 volt battery may be substituted for a power
  supply.
• A microphone must be connected to a transceiver
  for voice operation.
• A telegraph key is needed for CW operation.
• An electronic keyer can be used to help form good
  morse code characters.
• A dummy antenna (load) is used to adjust or
  troubleshoot a transmitter without transmitting a
  signal.
• If it is used with a 100-watt, SSB phone
  transmitter it should have a minimum rating of
  100 watts continuous.

19
More Station Accessories

• A duplexer is used to connect a dual-band
  transceiver with separate VHF UHF outputs to a
  dual-band antenna.
• Most dual-band transceivers cover 2 meters and
  70 cm.
• A power amplifier may be useful to boost the
  low-power output from a hand-held transciever up
  to 100 watts.
• An SWR meter may be connected between a
  transceiver and an antenna switch connected to
  serveral antennas to check monitor the match to
  the antenna.

20
Station Layout
2
3
1
ANTENNA SWITCH
DUMMY ANTENNA
TRANSCEIVER
An antenna switch can be used to connect the
transceiver to one of several antennas or to a
dummy antenna.
21
Station Layout
2
3
1
SWR METER
ANTENNA TUNER
TRANSCEIVER

• An Antenna Tuner connects directly to an antenna
  and allows an antenna to be used on a band it was
  not designed for.
• An SWR Meter is used to measure the standing wave
  ratio and can be used to properly adjust an
  antenna tuner.

22
Coaxial Cable

• Coaxial cable has a center wire inside an
  insulating material covered by a shield and an
  insulating cover.
• Good quality coax should be used for a UHF
  antenna system to keep RF loss low.
• Radio energy is converted to heat in a poor
  quality coaxial cable.
• Coax is Unbalanced Feedline in that one conductor
  is connected to ground.

23
Parallel-Conductor Feed Line

• Consists of two wires held apart by insulating
  material.
• Parallel-conductor, open wire feed line will
  operate well even with high SWR and has less loss
  than coax.
• Parallel-conductor feedline is balanced.

24
Concept of Standing Wave Ratio

• If an antenna system matches the characteristic
  impedance of the transmitter all the power is
  radiated. Power travelling from the transmitter
  to the antenna is called Forward Power.
• If an antenna system does not match the
  characteristic impedance of the transmitter, some
  of the power is reflected back to the
  transmitter. This is called Reflected Power.
• At any point along the transmission line, the
  Forward Power and Reflected Power will add or
  subtract.
• The Ratio of the Maximum Voltage to Minimum
  Voltage along the line is called Standing Wave
  Ratio (SWR).

1 Volt
0.5 Volt
R1.5/0.5 3
25
Calculation of SWR

• Visualize a coax with a slot in it so that a
  voltmeter probe can be inserted.
• Slide the probe along the line and record the
  maximum and minimum voltage.
• Calculate the ratio of maximum to minimum voltage.

V Max 1.5 V Min 0.5 SWR VMax/VMin
1.5/0.5 3
26
SWR Analysis

• An SWR of 11 would indicate the impedance of the
  antenna and its transmission line are matched.
• An SWR of 41 would indicate an impedance
  mismatch something may be wrong with the antenna
  system.

• If a directional RF wattmeter has a forward power
  reading of 90 watts and a reflected power reading
  of 10 watts the actual transmitted power would be
  80 watts.
• Most RF wattmeters operate with a line impedance
  of 50 ohms.

27
The Antenna Tuner
Antenna Tuners do not really tune
antennas. They provide an impedance match between
the transmitter output impedance and the antenna
system impedance.
28
The Balun

• Balun means BALanced to Unbalanced.
• The balun converts from balanced feed line to
  unbalanced feed lines.
• A balun would be installed between the coax and
  the antenna to feed a dipole antenna with 50-ohm
  coax.

29
The 1/2 Wave Dipole
½ wavelength by formula
Feed Point
Coax
The physical length of a dipole and other
antennas can be reduced without changing its
resonant frequency by adding a loading coil.
30
The 1/2 Wave Dipole
Radiation pattern for a dipole antenna looking
down from above the antenna. If the ends of a ½
wave dipole antenna point east and west most of
the radio energy is radiated north and south.
31
The 1/4 Wave Vertical
Feed Point
¼ Wave
234 f (MHz)
Length of vertical in feet
¼ Wave Radials
32
½ Wave ¼ Wave Excercise

• A half-wave dipole for 147 MHz ?? inches
• A half-wave dipole for 223 MHz ?? inches
• A quarter-wave vertical for 146 MHz ?? inches
• A quarter-wave vertical for 440 MHz ?? inches

37 inches
25 inches
19 inches
6 inches
33
The Yagi
1
Feed Point
2
3
Driven Element
The Driven Element is approximately ½ wavelength
long. The Boom length has the greatest effect on
the gain of a Yagi.
Boom
Gain
Director
Reflector
Feedline
34
The Yagi

• The yagi antenna focuses RF energy in one
  direction, giving the appearance of getting free
  power.
• This free power is called Antenna Gain.
• If an antenna has a gain of 3 dB the effective
  radiated power will double.
• Many yagis are multiband antennas allowing them
  to operate on several bands with a single feed
  line.

35
Cubical Quad Antenna

• A cubical quad has two or more parallel
  four-sided wire loops, each approximately
  one-electrical wavelength long.

36
Radio Wave Polarization

• With horizontal polarization the electric lines
  of force of a radio wave are parallel to the
  Earth's surface. Horizontal antennas produce
  horizontal polarization.
• With vertical polarization the electric lines of
  force of a radio wave are perpendicular to the
  Earth's surface. Vertical antennas produce
  vertical polarization.
• Most VHF and UHF repeater antennas use vertical
  polarization.
• Most weak signal VHF / UHF SSB operation is done
  with horizontal polarization.
• Most satellite operation uses circular
  polarization.

37
VHF / UHF Antenna Considerations

• Most hand-held transceivers come with a rubber
  duck antenna which is much less efficient than a
  quarter-wavelength telescopic antenna.
• The operation of a hand-held transceiver in a
  vehicle will be greatly improved by using an
  external antenna on the vehicle roof.

38
Ammeter

• An ammeter measures current.
• An ammeter is connected in series with the
  circuit under test.

Ammeter
Power Supply
Transceiver
39
Voltmeter

• A voltmeter is used to measure electromotive
  force.
• A voltmeter is connected in parallel with the
  circuit under test.
• When you switch a voltmeter to a higher range
  resistance is added in series with the meter.

Voltmeter
Power Supply
Transceiver
40
Ohmmeter

• An ohmmeter is used to measure DC resistance.

Ohmmeter
41
Multimeter
Multimeters will measure Voltage, Current and
Resistance. Be sure it is set properly to read
what is being measured. If it is set to the ohms
setting and voltage is measured the meter could
be damaged!
42
Meter Excercise
What circuit quantity would meter A indicate?
R
Battery voltage
What circuit quantity would meter B indicate?
The current flowing through the resistor
43
Power
Power is measured in Watts
W E x I
Ohms law states E I x R
So, for this circuit, the power consumed in the
resistor can be calculated by multiplying the
value of the resistor times the square of the
reading of Meter B.
44
Soldering Safety

• When using a soldering iron or gun keep in mind
  the following safety considerations
• A soldering iron gets very hot, make sure no one
  touches it for at least 10 min after turning it
  off.
• Wear safety glasses, occasionally molten solder
  will splash.
• Solder in a well ventilated area. The fumes can
  be hazardous.

45
Basic Troubleshooting

• If a rig works in the car but not in the house
  the first thing to check is the power supply.
• If a mobile transceiver does not power up check
  the 12 volt fuses.
• If it is suspected the supply voltage to a rig is
  low, check the voltage with a voltmeter at the 12
  volt plug on the rig rather than at the power
  supply or battery.

46
More Basic Troubleshooting

• If AC hum is reported on a CW transmitter's RF
  signal additional filtering of the power supply
  may be required.
• Stray noise and RF pick-up may be reduced by
  providing adequate DC source supply filtering for
  a mobile transceiver.
• A signal generator produces a stable, low-level
  signal that can be set to a specific frequency
  and may be useful for checking a receiver.

47
Homework

• Study Subelement T8 of the question pool.
• Read the Question and the Answer Three Times.
• Read Chapter 8 in Now You're Talking.